The present invention relates to an automatic welding machine for planar plastic materials, having a chassis and, arranged thereon, a welding device, a driving unit, a pressure device for the materials welded in an overlapping manner.
Such automatic welding machines are generally known and are in use, and are used for welding tarpaulins of coated fabrics, films and sealing sheets of PVC-P, PE, ECB, CSPE, EPDM, PVDF, etc., and also PE-coated band fabrics for trucks, tents, covers in agriculture, biotopes, swimming pools, awnings, boat tarpaulins, inflatable boats, advertising tarpaulins, etc. Further similar materials occur in civil engineering, roof construction and flooring. These materials are referred to below as (planar) plastic materials. The plastic materials are arranged in an overlapping manner for welding, so that the two plastic materials lie one on top of the other in an overlap region and are referred to as a top plastic material and as a bottom plastic material. It is also possible for the plastic materials which are to be welded to one another to be placed in an abutting relationship and for a strip which covers both bottom layers in an overlap region to be welded to the respectively bottom plastic material. The known automatic welding machines can be used here too.
Hot-air welding sets, hot-wedge welding sets or a combination thereof may be used as the welding devices.
An automatic welding machine as is used in particular for welding plastic sealing sheets on roofs is shown in EP-A-1-946 057. These known automatic welding machines obtainable on the market have a chassis, on which a welding device is arranged such that it can be swiveled from a rest position into a working position. Furthermore, these automatic welding machines have transport rollers, with which the automatic welding machine is moved into the respective working position and aligned with the weld. According to the prior art, these transport rollers are adjustable in the vertical direction at least in the rear region by means of a mechanism in order to be able to take the weight of the automatic welding machine off the transport rollers in the welding position and transfer it to the driving unit and the pressure device. In the known device, the driving unit and the pressure device are combined in a driving and pressure roller. In the known sets, a guide wheel is located as guide device in the front region, this guide wheel performing a pointer function during the welding operation in order to show the track which is just being welded to the operator. The guide wheel does not take up any weight.
Furthermore, automatic welding machines for welding plastic films are known in which the welding device is arranged directly on the housing and which therefore has a (steerable) transport roller with respect to the rear driving and pressure rollers.
With automatic welding machines used for plastic tarpaulins or films, i.e. relatively thin and fine materials, there is the problem that, despite accurate adjustment of the automatic welding machine along the weld, the automatic welding machine has to be corrected again and again with regard to the track. The result of this is that the welded joint, simply in its appearance, constitutes more of a slalom line, and furthermore folds develop due to the partly oblique movement by means of the driving/pressure roller along the edge of the overlapping material.
The object of the present invention is therefore to propose an automatic welding machine which largely keeps to the track and thus ensures increased weld quality.